With regard to this question, assuming it is decided that a monk can use unarmed attacks "off-hand" in two-weapon fighting, does a monk using the standard rules for two-weapon fighting with "off-hand" unarmed attacks get 1x or 0.5x strength bonus on said attacks?
The rules are worded weirdly, and I will disagree with KRyan, and the FAQ, on their reading. Woe is me...
TL;DR: If the Monk chooses to use Two-Weapon Fighting, she may use her full Strength modifier with her off-hand unarmed strike.
First, we need to consider the regular rules. For Damage (PHB, p. 135):
If you score a hit, roll damage and deduct it from the target’s current hit points. Add your Strength modifier on damage rolls involving melee and thrown weapons. If you’re using a weapon in your off hand, add one-half your Strength modifier (if it’s a bonus). If you’re wielding a weapon with both hands, add one and a half times your Strength modifier (if it’s a bonus.)
For Two-Weapon Fighting (PHB, p. 160):
If you wield a second weapon in your off hand, you can get one extra attack per round with that weapon. [...] You can reduce these penalties in two ways:
- If your off-hand weapon is light, the penalties are reduced by 2 each. (An unarmed strike is always considered light.)
- The Two-Weapon Fighting feat lessens the primary hand penalty by 2, and the off-hand penalty by 6.
From this, we conclude that:
- If you wield a second weapon in your off hand, you can get one extra attack per round with that weapon.
- There are penalties for attacking with your off-hand, and you only get to add 1/2 your Strength modifier as bonus to damage.
As noted by KRyan's answer to the question you linked, there is the issue that technically one needs to wield a weapon in one's off hand to gain one extra attack, and one wishing to make an Unarmed Strike typically doesn't -- though the Monk could.
From the highlighted excerpt about an Unarmed Strike always being considered Light, which only makes sense if making an Unarmed Strike with the off-hand is possible in the first place, I interpret the rules as allowing using Two-Weapon Fighting without wielding a weapon in one's off-hand.
Then we need to consider the Monk's Unarmed Strike (PHB, p. 41):
Unarmed Strike: Monks are highly trained in fighting unarmed, giving them considerable advantages when doing so. [...] There is no such thing as an off-hand attack for a monk striking unarmed. A monk may thus apply her full Strength bonus on damage rolls for all her unarmed strikes.
Invoking the principle that context is everything, I will consider the two last sentences together.
In isolation, the first sentence does not make much sense. "striking unarmed" or "strike unarmed" appears nowhere else in the PHB. The proper game term would be "making an Unarmed Strike", which is used consistently.
By reading the first sentence in light of the second sentence, however, it all makes sense:
- The second sentence grants the Monk the benefit of using her full Strength modifier with all Unarmed Strikes; thereby overriding the Damage rule for off-hand damage in this case.
- The first sentence therefore introduces the second sentence: it's an opening line, in plain English. Just fluff, with no game consequences.
And in this light, the formulation of the first sentence makes sense:
- Plain English sentences are not restricted to using game terms, so "striking unarmed" is not an issue.
- When the Monk makes an Unarmed Strike with her off-hand, it deals the same amount of damage as a regular attack... as if it were a regular attack. As if it was not an off-hand attack. Hence, from an observer, "There is no such thing as an off-hand attack for a monk striking unarmed", all attacks are indistinguishable.
Hence, as a result:
- It is permissible to use Two-Weapon Fighting without wielding a weapon in your off-hand, in which case the extra attack is an Unarmed Strike.
- All Unarmed Strikes from a Monk apply the Monk's full Strength modifier to damage, as a special case overriding the regular 1/2 Strength modifier on off-hand attacks.
I must warn, though, that the result is less than stellar:
- Flurry of Blows gives: -2/-2 at the start, -1/-1 starting from 5th level, no penalty from 9th level, and an additional attack from 11th level.
- Two-Weapon Fighting gives: -4/-8 in the absence of the feat, and -2/-2 with it.
Furthermore, Flurry of Blows also grants the full Strength modifier for the "bonus" attacks even when attacking with Special Monk Weapons.
There is the Two-Weapon Feat fighting line, which for the cost of 3 feats would allow a Monk 15 (or higher) to make 3 more attacks, however it uses iterative attack penalties for the extra attacks, on top of the -2 penalty, so even then seems less attractive than only 2 extra attacks at full BAB. Especially on a BAB-starved class.
I know, it’s very controversial whether one should use the 3.5 Main D&D FAQ as a source for rules clarifications (see here). But since there are two entries (pages 19, 20) that directly address the above question, I think it’s worth taking a look at them.
According to the FAQ a monk can indeed use unarmed attacks off-hand in two-weapon fighting with the off-hand attack gaining only half Strength bonus to damage. It's also possible to combine Flurry of Blows and TWF.
The rules don’t come right out and say that a monk can’t use an unarmed strike for an off-hand strike (although the exact wording of the unarmed strike ability suggests otherwise), and no compelling reason why a monk could not do so exists. When using an unarmed strike as an off-hand attack, the monk suffers all the usual attack penalties from two-weapon fighting (see Table 8–10 in the PH) and the monk adds only half her Strength bonus (if any) to damage if the off-hand unarmed strike hits.
A monk can fight with two weapons just like any other character, but she must accept the normal penalties on her attack rolls to do so. She can use an unarmed strike as an offhand weapon. She can even combine two-weapon fighting with a flurry of blows to gain an extra attack with her off hand (but remember that she can use only unarmed strikes or special monk weapons as part of the flurry). The penalties for two weapon fighting stack with the penalties for flurry of blows.
That would seem to be consistent with the ruling you assume in the question.
The source of this confusion is this:
There is no such thing as an off-hand attack for a monk striking unarmed. A monk may thus apply her full Strength bonus on damage rolls for all her unarmed strikes.
It’s not at all clear why this sentence exists or what it really means. The literal meaning of the words—that the monk loses the ability to make offhand attacks with unarmed strikes—makes no sense at all since the sentence prior to this is
A monk’s attacks may be with either fist interchangeably or even from elbows, knees, and feet. This means that a monk may even make unarmed strikes with her hands full.
They are emphasizing here that a monk is good at making more attacks with unarmed strikes—why would they therefore be incapable of doing so? And if we assume that this doesn’t mean they’re incapable of doing so—as the question does—what else could these sentences mean?
The only reasonable explanation that I can imagine is that they were imagining the monk making these attacks as part of a flurry of blows; they seem to never consider the idea that a monk may want to use two-weapon fighting when they have flurry of blows available. The rules for flurry of blows make the same statement about using 1×Str for damage rolls—not ½×, as for an offhand attack, and not 1½×, as for a two-handed attack—and it would be very appropriate and consistent for flurry of blows to specify that none of the attacks made during a flurry of blows are considered offhand.
Unfortunately, that’s not where they put the rule. They put the rule in unarmed strikes, and that causes immense confusion.
Anyway, assuming you don’t buy that a monk’s mastery of unarmed strikes makes them somehow incapable of using them with two-weapon fighting, it makes sense for you to ignore the other “half” of that blurb and apply the ½×Str to damage, too. Otherwise what we’re doing is selectively ignoring the rule we don’t like (“There is no such thing as an off-hand attack for a monk striking unarmed.”) while still taking advantage of the rule we do even though it builds off the rule we’re ignoring (“A monk may thus apply her full Strength bonus on damage rolls for all her unarmed strikes,” emphasis mine), which is inconsistent. If we’re going to ignore it, we should do so consistently.
Of course, if we want to take this beyond the realm of “ruling” and into outright “houserules,” allowing the monk to make offhand unarmed strikes, and still get full Str bonus to damage on them, is entirely reasonable: the monk is a terrible class and it’s a bone we can easily toss them. Won’t fix the problems with the monk class on its own, though, not by a long shot.